It has been known to apply a soft magnetic powder material which includes a powdered soft magnetic material (i.e., principal ingredient is high purity iron powder) and a powdered resin as a material for constructing a magnetic path forming member such as motor core (e.g., a rotor core and a stator core). By applying the pressure and the heat to the soft magnetic powder material, a soft magnetic green compact is formed. The powdered resin includes a binding function to connect iron system powdered particles and an insulating function for electrically insulating between the iron system powdered particles. By electrically insulating between the iron system powdered particles, an electric characteristic (e.g., resistivity) becomes favorable when an alternating-current magnetic field affects the soft magnetic green compact and the eddy current loss of the soft magnetic green compact can be reduced.
Advantages for forming the soft magnetic powder material with a die are as follows, which includes a high yield which reduces the manufacturing cost; the high flexibility of the soft magnetic green compact compared to a method for accumulating the steel plate, which reduces the size of the soft magnetic green compact and reduces the manufacturing cost; reducing the processes, which reduces the manufacturing cost; and the high recycling efficiency compared to the method or accumulating the steel plates, which contributes to the environmental conservation and to utilize the resources effectively.
Notwithstanding, there are disadvantages for forming the soft magnetic powder material. First, it is difficult to ensure the strength of the soft magnetic green compact formed with the soft magnetic powder material, particularly, under the high temperature condition because the resin is included in the soft magnetic powder material.
Second, because the resin included in the soft magnetic powder material is adhered to a cavity surface of the die when applying the heat, it is necessary to devise to easily remove the soft magnetic green compact made of the soft magnetic powder material from the die.
Third, although the electric characteristic (e.g., resistivity) as the soft magnetic material is improved by the addition of the powdered resin in the soft magnetic powder material, the magnetic characteristic (e.g., the magnetic permeability, saturation flux density) is declined because the resin is deficient in the magnetic permeability. Thus, it is required to strike a balance between the electric characteristic and the magnetic characteristic at high level.
As explained above, because high strength under the high temperature condition is not achieved, the known soft magnetic green compact made of the known soft magnetic powder material has not applied to members such as motor core which requires high strength under the high temperature condition.
The second drawback of forming the soft magnetic green compact made of the soft magnetic powder material may be obviated by lubricating the cavity surface of the die and by mixing the lubricant in the soft magnetic powder material per se. However, in this case, there are the drawbacks that the manufacturing cost is increased, the productivity is reduce, and the strength of the soft magnetic green compact is reduced by adding and applying the lubricant.
A need thus exists for a soft magnetic powder material, soft magnetic green compact including the soft magnetic powder, and a manufacturing method of the soft magnetic green compact which enables to achieve the high strength under the high temperature condition, to be easily ejected from a die, and to strike a balance between the magnetic characteristic and the electric characteristic.